Method and system for improving vision

ABSTRACT

Methods and apparatus for improving vision incorporate the effects of biodynamical and biomechanical (biological) responses of the eye. The eye produces a biological response to trauma, such as a LASIK keratectomy or other necessary traumatic procedure in preparation for refractive surgery. By observing the biological response, a prospective treatment to correct higher order aberrations is adjusted to compensate for the biological effects. An improved photorefractive surgery system incorporates one or more suitable diagnostic devices that provide biological response information in such a manner that the patient need not change position from that assumed for the surgical procedure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of Ser. No. 10/045,694 filed Oct. 19,2001 now U.S. Pat. No. 6,926,710.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to methods and apparatus forphotorefractive correction of vision, and more particularly to theadjustment of higher order aberrations in consideration of biodynamicaland biomechanical responses of the eye.

2. Description of Related Art

The field of photorefractive surgery for vision correction continues togrow rapidly. The number of procedures demanded by consumers isconstantly increasing at the same time that researchers andpractitioners are learning more about vision and how to correct it. Theapplication of excimer laser technology including refinements in beamsize, shape, and placement, active eye tracking, and diagnosticinstrument development including topographers, wavefront sensors,ultrasound, and OCT's underscores the progress in this field.

What has become evident as understanding continues to unfold about whatperfect vision really is, is that models need to be developed whichdescribe the eye and its various responses to attempts at visioncorrection. The advent of wavefront sensing in ophthalmology is drivingnow traditional procedures such as photorefractive keratectomy (PRK) andLASIK which were primarily concerned with correcting refractive errorssuch as defocus and astigmatism (myopia, hyperopia, and astigmatic formsthereof), to the investigation and performance of more sophisticatedprocedures in which higher order optical aberrations (herein referred toas third and higher Zernike order or equivalent) are being addressed.These higher order monochromatic aberrations include, for example,spherical aberration, coma, and others as well understood by thoseskilled in the art.

The inventors of the present invention have recognized that directlyeliminating all wavefront aberrations of the eye is not necessarily thekey to emmetropia, because the act of photorefractive correction itselfinduces certain defects that must be accounted for in developing aphotorefractive treatment. Accordingly, the invention is directed tomethods and apparatus for developing and performing photorefractivetreatments in view of these observations and which result in betterobjective and subjective visual evaluation.

SUMMARY OF THE INVENTION

Various embodiments of the invention are directed to methods andapparatus for improving vision by correcting higher order opticalaberrations of the eye in consideration of biodynamic and biomechaniceffects and responses of the eye.

In an embodiment of the invention, a method for developing aphotorefractive treatment of a patient's eye involves making adiagnostic measurement to determine lower (second Zernike order orbelow) and/or higher (third and higher Zernike order) opticalaberrations and adjusting a prospective photorefractive treatment basedupon an expected, observed, calculated or otherwise anticipatedbiodynamical and/or biomechanical effect. Such an effect induces adeviation from an expected result of the prospective treatment in theabsence of such biodynamical and/or biomechanical induced deviation.This adjustment will advantageously be a calculated or derivedadjustment, however, empirical adjustments are entirely suitable as theyform a basis for building and/or validating biodynamical andbiomechanical models of the eye. Diagnostic measurements of the eyeinclude directly measured or derived wavefront aberration measurements,topographic measurements including surface contours, eye componentthicknesses, decentration, line of sight, height variation, etc., OCTmeasurements, ultrasound, and pachymetry measurements. The developedphotorefractive treatment preferably includes photoablation by anexcimer laser having appropriate beam sizes, shapes, and placements.Laser beam diameters at a target surface on the eye preferably rangebetween 0.5 mm to 7 mm and may include different, multiple beamdiameters within this range. In an aspect of this embodiment, furtherdiagnostic measurements are made that are indicative of the shape of thestromal surface of the patient's eye which underlies the epithelium, forexample, the stromal surface shape below a LASIK flap or non-uniform orotherwise abnormal thickness epithelial layer. Based upon empiricalobservations to date, it is preferable that the sum total ofrotationally symmetric aberrations, e.g., spherical aberration, be equalto or greater in magnitude than the sum total of rotationally asymmetricaberrations, e.g., coma.

In another embodiment of the invention for correcting higher orderaberrations of a patient's eye, a method comprises the steps of makingany necessary physical intrusions upon the eye as, for example,keratectomy for a LASIK procedure, hereinafter referred to as trauma tothe eye; obtaining diagnostic wavefront information at some time afterthe infliction of the trauma; and developing a photorefractive treatmentfor correcting the higher order aberrations of the patient's eye basedat least in part upon the subsequent wavefront information. Thewavefront information can be directly obtained by a wavefront measuringinstrument or derived through indirect measurements based upontopography or other diagnostics as one skilled in the art willunderstand. In this exemplary embodiment, the LASIK cut is made but theflap is not lifted prior to making the diagnostic wavefront measurement.When the necessary trauma is inflicted upon the eye, the eyes biologicalresponse will show up as wavefront aberrations that are different fromthe wavefront aberrations of the eye prior to inflicting the trauma. Inaddition, the effect of the trauma as determined by corneal topographicmeasurements of corneal thickness and the anterior and especiallyposterior surfaces (where the effect is the largest), can be used topredict the total biomechanical response once the photo-ablativeprocedure is complete. Based upon an observed, derived, calculated orotherwise obtained indication of the biological response of the eye, aprospective treatment profile based upon an unconsidered biologicalresponse is modified to compensate for biological effects. The durationof time between inflicting the trauma and making the diagnosticmeasurement to obtain wavefront information will depend at least in partupon the severity, nature and extent of the biological effect inresponse to the trauma. It will therefore be appreciated by thepractitioner what a suitable duration will be. In an aspect of thisembodiment, a biomechanical effect can also be used to adjust thedeveloped treatment. Non limiting examples of biodynamical effectsinclude edema and epithelial growth, while a non-limiting example of abiomechanical effect is epithelial hole filling due to eyelid pressure.Biomechanical effects can be discerned from, for example, epithelialthickness measurements using high frequency ultrasound as described inthe literature. It is again preferable based on empirical observationthat the resultant sum total of the rotationally symmetric aberrationsequal or exceed the sum total of the rotationally asymmetric opticalaberrations. These empirical observations appear to agree withsubjective patient evaluation and point spread function analysis inevaluating vision improvement. It is preferable to make the diagnosticmeasurements along the line of sight of the patient's eye and, asbefore, to perform photoablative treatments with laser beams havingfixed or variable diameter spots at the eye target between about 0.5 mmand 7 mm.

In an alternative aspect of this embodiment, a corneal inlay procedurecan also be appropriately adjusted based upon the biodynamical and/orbiomechanical effects in response to eye trauma. In fact, any refractiveprocedure will benefit from consideration of biological effects inresponse to the proposed treatment.

A method according to the invention also applies to reducing regressionafter photorefractive surgery such as, e.g., PRK or LASIK. Inparticular, consideration of the biodynamic effect which results in afilling in of high frequency variations in the treated eye surfaceassociated with correction of higher order aberrations can be used tomodel the eye and adjust a treatment procedure for vision correction.

In a further embodiment according to the invention, a system forperforming refractive surgery is improved by including a diagnosticmeasurement instrument such as, e.g., a wavefront measuring instrument,to the photoablative laser system such that the desired diagnosticmeasurement on the patient's eye can be made while the patient is in thesame position as when the necessary eye trauma is inflicted for theintended surgical procedure. This has a non-limiting benefit of, e.g.,removing the effects of eye rotation that occurs when a patient changesfrom a sitting to a supine position.

The foregoing features, advantages, and objects of the invention aredescribed and illustrated in the detailed description and figures whichfollow and as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating the process steps according to anembodiment of the invention;

FIG. 2 is a flow chart illustrating the process steps according to anembodiment of the invention;

FIG. 3 is a schematic illustration of a photorefractive surgery systemaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The invention relates generally to methods and apparatus forphotorefractive treatment to correct or improve vision. In particular,the invention relates to methods and apparatus for developing andcarrying out photorefractive treatments related to higher orderaberrations in consideration of biodynamical and biomechanical effectson treatment.

FIG. 1 shows a series of method steps 10 according to an embodiment ofthe invention. As illustrated, a diagnostic measurement of a patient'seye is obtained at step 12. This diagnostic measurement 12 is used todetermine an optical aberration of the eye in step 14, preferably, butnot limited to, a higher order, monochromatic aberration. As that termis used herein, higher order aberration refers to third and higher orderZernike coefficients or their equivalents, while lower order aberrationssuch as defocus and astigmatism are represented by second and lowerorder Zernike coefficients or their equivalents. Based generally on pastempirical data or other prior information, a prospective treatment 16 isformulated to address the aberrations identified in step 14. Theprospective treatment 16, however, is adjusted based upon biodynamicaland/or biomechanical effects that are either anticipated, observable,and/or known that would result in the prospective treatment 16 providingless than optimum results in terms of improved vision for the patient.The treatment that is developed in step 20 thus takes into account thebiodynamical and/or biomechanical effects that could induce a deviationof the desired result from the prospective treatment. It will beappreciated by those skilled in the art that adjustments to thetreatment based upon biodynamical and/or biomechanical effects will tendto be empirically based until enough information is collected toassemble models with more verifiable outcomes. According to aspects ofthis embodiment, the diagnostic measurement of step 12 can be a directwavefront measurement such as can be obtained by various wavefrontsensors, e.g., ZyWave (Technolas/Bausch & Lomb, Rochester, N.Y.), or byusing other diagnostic instruments and techniques such as, for example,topography data from an Orbscan II™ topographer (Orbtek/Bausch & Lomb,Rochester, N.Y.), ultrasound, optical coherence tomography (OCT),pachymetry, and others from which wavefront information can be derivedor other useful information can be obtained and which will guidedevelopment of a photorefractive treatment. A wavefront measurement isadvantageous in that the developed treatment comprises photoablationpatterns that may be developed in conjunction with individual aberrationorders. The treatment protocol may be single stage or a multi stagetreatment such as that described in co-pending application entitled“Method and Apparatus for Multi-Step Correction of Ophthalmic RefractiveErrors” filed on Oct. 20, 2000 and incorporated herein by reference inits entirety. That application describes a multi-stage, convergingsolution approach to photorefractive surgery in which an initialablation corrects gross defects while a second stage (or subsequentstages) relies, preferably, on a known nomogram for correcting theresidual defect.

In an aspect of this embodiment, another diagnostic measurementrepresented at step 24 can be carried out to further evaluate thebiological response of the eye. As illustrated by example in FIG. 1, thestromal/epithelial interface may be measured as well as the stromalprofile and/or epithelial thickness which is advantageous because thestroma is the ultimate treated surface in a LASIK procedure, forexample. Ultrasonic and OCT techniques are known to obtain these typesof measurements.

Performance of the developed treatment is typically carried out using anexcimer laser having a wavelength of 193 nm with a fixed or variablebeam size of between 0.5 mm to 7 mm in diameter at the target surface.Such lasers are exemplified by the Technolas 217 laser system and theTechnolas Zyoptics™ laser vision correction system. Regardless of thedevice used to perform the developed treatment, based upon empiricaldata, it has been observed by the inventors that a patient's best visionis obtained when the patient's point spread function is optimized and,or alternatively, the sum total of the residual rotationally symmetricaberrations equals or is greater than the sum total of the residualrotationally asymmetric aberrations, in contrast to hypotheticaloutcomes of zero wave aberrations.

Another embodiment according to the invention is illustrated inconnection with the flow diagram shown in FIG. 2. A method forcorrecting higher order aberrations of a patient's eye 10 includes thebasic process steps of inflicting a surgical trauma to the eye 120corresponding to a particular ophthalmological procedure; i.e.,keratectomy or lamellar cut to create a LASIK flap, for example. Otherexemplary traumas include corneal scraping, puncture, etc. Diagnosticwavefront information 140 is then obtained subsequent to inflicting thetrauma in step 120. A treatment 160 is developed based upon thesubsequent diagnostic wavefront information 140. Due to the biologicalnature of the eye, a biodynamic and/or biomechanical effect 180 isproduced in response to the trauma and this biodynamic/biomechaniceffect 180 in the form of empirical data, derived data, modeled data, orwhatever suitable form the information exists in, can be considered indeveloping the photorefractive treatment for correcting the higher orderaberrations of the patient's eye. In fact, the subsequent diagnosticwavefront information 140 will be indicative to some degree of thebiodynamic or biomechanical effect produced in response to the surgicaltrauma.

An advantageous aspect of this embodiment resides in the optional stepof making a prior diagnostic measurement 145 (prior to the surgicaltrauma) and using the prior diagnostic information in conjunction withthe subsequent diagnostic information to develop the photorefractivetreatment. For example, the prior diagnostic measurement 145 may provideinformation about ocular decentration. Such decentration, for example,if unnoticed before the keratectomy, would result in a biodynamicresponse having different effects than a symmetric keratectomy. Whenthis information is used in connection with directly obtained or derivedwavefront information, a prospective treatment can be adjusted basedupon biodynamics and/or biomechanics to develop the ultimate treatment160.

The duration of time between inflicting the surgical trauma andobtaining the subsequent diagnostic wavefront information will beempirically or diagnostically determined by the skilled practitioner.That time suitably will range between immediately after the surgicaltrauma to as long as one month after the trauma infliction, butpreferably sooner rather than later.

Another aspect of this embodiment is illustrated at step 185 wherein anexemplary stromal diagnostic measurement is made to determine theepithelial thickness, stromal profile, or other characteristics whichimpact or are indicative of a biodynamical effect. This information canthen be used in conjunction with the subsequent diagnostic wavefrontinformation 140 and, if obtained, the prior diagnostic measurementinformation 145 to adjust a prospective treatment profile in order todevelop the ultimate treatment 160. Finally, the treatment is carriedout at step 190. As referenced above, empirical data suggests that mostpatients are happier about their corrected vision when a residual sumtotal of rotationally symmetric aberrations equals or exceeds a residualsum total of rotationally asymmetric aberrations, as opposed to zeroresidual aberrations or some other combination of residual higher orderaberrations.

Although the method embodiment described above relates generally to aphotoablative treatment of the eye, it will be appreciated by thoseskilled in the art that the method also lends itself to a corneal inlayprocedure. In fact, any surgical vision correction or vision improvementprocedure would benefit from consideration of biodynamic andbiomechanical effects produced in response to any aspect of the surgicaltreatment.

Another embodiment according to the invention describes a method forlessening regression that often results after photorefractive treatmentof a patient's eye. The method basically consists of adjusting aprospective treatment for modifying an optical aberration of thepatient's eye in consideration of at least a biodynamic or abiomechanical effect of the eye in response to any portion of theprospective treatment. Such biodynamic effects include, but are notlimited to, epithelial growth, edema, and other biological responses,while the biomechanical effects are understood to include but not belimited to the effect of eyelid pressure on stromal smoothing. Forexample, it is postulated that when higher order aberrations areaddressed by photoablation, a high frequency variation in the treatedstromal surface results. However, over time these high frequencyvariations are filled in by epithelial cells that are constantly pushedand scrapped by the pressure of the eyelid during the blinking response.Ultimately, empirical data suggests that whatever adjustments are made,the residual sum total of the rotationally symmetric aberrations shouldequal or exceed the residual sum total of the rotationally asymmetricaberrations.

FIG. 5 shows a system embodiment 500 according to the invention. Thesystem 500 is an improved system for refractive surgery on a patient'seye. Conventional systems include a laser system 510 suitable forphotorefractive correction of eye tissue. A computer 520 is typicallylinked to the laser system 510 and is used, at least in part, to developthe photorefractive treatment. A laser control system 530 is linked tothe laser system and the computer to control the firing of the laser. Aviewing system 540, typically in the form of a microscope and/or displayscreen, for example, is further linked to the laser system forvisualization of the patient's eye during treatment by the practitioner.A suitable platform 550 is provided to situate the patient in thesurgical position, typically a supine position. Additionally, many ofthe refractive surgery systems include an eyetracker 570. The computer520, control system 530, viewing system 540, and platform 550 may beseparated from or integrated with the refractive surgery system. Theimprovement according to the invention includes a diagnostic measuringinstrument 560 that is linked to the system in such a manner that thepatient need not change their position from the surgical position inorder to obtain the diagnostic information. For example, a wavefrontsensor, a topography unit, an ultrasound unit, a pachymetry device, aOCT device or other suitable diagnostic instrument or any combinationthereof, could be positioned in the refractive surgery system overheadof the patient and aligned to the patient's line of sight to coincidewith the photorefractive treatment alignment. Alignment techniques andsystems for the laser system and one or more diagnostic instruments aredescribed in co-pending patent application entitled “Customized CornealProfiling” filed on Oct. 20, 2000 and incorporated herein by referencein its entirety.

While various advantageous embodiments have been chosen to illustratethe invention, it will be understood by those skilled in the art thatvarious changes and modifications can be made therein without departingfrom the scope of the invention as defined in the appended claims.

1. A method for developing a photorefractive treatment of a patient'seye, comprising: obtaining a diagnostic measurement of the patient'seye; using the diagnostic measurement to determine at least one of alower-order and a higher-order aberration of the eye; developing aphotorefractive treatment by adjusting a prospective photorefractivetreatment for the at least one aberration based upon at least one of abiodynamically and a biomechanically induced deviation from an expectedresult of the prospective treatment in the absence of the biodynamicallyor biomechanically induced deviation to compensate for said deviation;and performing a photorefractive treatment on the eye based on theadjusted prospective photorefractive treatment.
 2. The method of claim1, wherein said adjustment is an empirical adjustment.
 3. The method ofclaim 1, wherein said diagnostic measurement includes at least one of awavefront aberration measurement, a topography measurement, an OCTmeasurement, an ultrasound measurement, and a pachymetry measurement. 4.The method of claim 1, wherein the photorefractive treatment comprisesan ablation pattern that is the sum of ablation patterns for each of acontributing aberration order.
 5. The method of claim 1, wherein saidtreatment is a multi-stage treatment.
 6. The method of claim 1, whereinsaid treatment is adapted to provide a sum total of rotationallysymmetric aberrations that is equal to or greater than a sum total ofrotationally asymmetric aberrations.
 7. The method of claim 1, furthercomprising obtaining another diagnostic measurement that is indicativeof a shape of a stromal surface of the patient's eye.
 8. The method ofclaim 1, wherein said diagnostic measurement is made through a line ofsight of the patient's eye.
 9. The method of claim 1, comprisingperforming a photoablative treatment with a laser beam having adiameter, d, at a target location between 0.5 mm<d<7 mm.
 10. The methodof claim 1, further comprising obtaining a diagnostic measurement of thepatient's eye prior to inflicting the surgical trauma.